A Francis turbine is used in a hydraulic machine, including a reversible pump-turbine, for power generation.
A conventional Francis turbine runner is described in U.S. Pat. No. 4,479,757. This conventional Francis turbine runner includes blades whose inlet (a leading edge) shape is curved toward a direction opposite to a rotating direction of a turbine operation from a band side to a crown side.
Another conventional Francis turbine runner is described in U.S. Pat. No. 6,135,716. This conventional Francis turbine runner includes blades whose outlet (a trailing edge) shape is curved toward a rotating direction of a turbine direction from a crown side to a band side. This conventional Francis turbine runner also includes blades whose inlet (a leading edge) shape is curved toward a rotating direction of a turbine operation from a band side to a crown side.
Those shapes of the blades of conventional Francis turbines are developed to improve a hydraulic efficiency or to reduce cavitations. Still there is room to develop the shape of the blades that improves the efficiency because of the recent development of technology in fields such as computational fluid dynamics.
Especially, it is known that secondary flow, which is a flow not being along a flow line, distorts a pressure distribution on the blades and results in loss of hydraulic efficiency.